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arXiv · 1408.2901

The Phase Diagram and Hardness of Carbon Nitrides

Huafeng Dong·Artem R. Oganov·Qiang Zhu·Guang-Rui Qian
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Abstract

Novel superhard materials, especially those with superior thermal and chemical stability, are needed to replace diamond. Carbon nitrides (C-N), which are likely to possess these charac- teristics and have even been expected to be harder than diamond, are excellent candidates. Here we report three new superhard and thermodynamically stable carbon nitride phases. Based on a systematic evolutionary structure searches, we report a complete phase diagram of the C-N system at 0-300 GPa and analyze the hardest metastable structures. Surprising- ly, we find that at zero pressure, the earlier proposed graphitic-C3N4 structure (P-6m2) is dynamically unstable and the lowest energy form of structures based on s-triazine unit and s-heptazine unit have similar topology and belong to the same space group.

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Huafeng Dong, Artem R. Oganov, Qiang Zhu, Guang-Rui Qian. 2014-08-13. The Phase Diagram and Hardness of Carbon Nitrides. https://doi.org/10.1038/srep09870

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